The rapid increase in vehicle traffic on the roads and the associated queues and travel time extensions are resulting in increased efforts worldwide to identify traffic states and to take them into account for the route selection or for route calculation in navigation systems.
If the geographical coordinates measured using a position-finding method are mapped directly to the coordinate system of a digital map, the true position of the object in the map may differ from the mapped position of the object in the map. The reason is firstly measurement errors in the position-finding method and secondly inaccuracies in the map. Since a navigation system needs to know the true position in the map, the map matching method aligns the measured position with the map information about the position and geometry of objects in the map, so that the most probable position of the object in the map is ascertained.
In vehicle navigation systems, the position of the vehicle is usually measured with the assistance of the satellite position-finding system GPS. The correctness of the measured and actual positions is specified at approximately 15 m in the case of GPS. Similarly, the digital map may have tolerances in the region of meters. For the navigation appliance, it is now necessary to ascertain the position of the vehicle in the digital map so that, by way of example, it is possible to determine a meaningful route calculation from the current location to the destination of travel. Without alignment of the measured position with the map information, the vehicle could find itself outside of the digitalized roads or on the wrong road in the map. Since the position of the vehicle in the digital map is critical for the navigation appliance, the measured position is aligned with the map information such that the most probable location of the vehicle in the map is ascertained for the navigation. In this regard, map matching involves utilizing the knowledge about the movements of the vehicle.
Digital maps are usually outdated as soon as they are delivered. For this reason, an update for the map is indispensible if the digital map is intended to correspond to the current circumstances. However, these updates comprise large volumes of data, since the whole map is always brought up to date.